This invention relates to the synthesis of an aliphatic 1,3-diol, particularly 1,3-propanediol, from ethylene oxide and syngas in one step. More particularly this invention relates to a catalyst that provides good yields under mild conditions in the one-step synthesis of 1,3-propanediol and demonstrates advantages with respect to cost and oxidative stability. The catalyst of the invention comprises a homogeneous bimetallic cobalt-ruthenium catalyst, plus a N-heterocyclic ligand, or multidentate N-heterocyclic ligand.
Aliphatic 1,3-diols, particularly 1,3-propanediol, have many applications as monomer units for polyester and polyurethane, and as starting materials for the synthesis of cyclic compounds. For example, CORTERRA(copyright) polymer is a polyester characterized by outstanding properties that is made of 1,3-propanediol (hereafter 1,3-PDO) and terephthalic acid. There is much interest in the art in finding new routes for synthesizing 1,3-PDO that are efficient, economical, and demonstrate process advantages.
U.S. Pat. Nos. 3,463,819 and 3,456,017 teach the hydroformylation of ethylene oxide to produce 1,3-propanediol and 3-hydroxypropanal (hereafter 3-HPA) using a tertiary phosphine-modified cobalt carbonyl catalyst.
U.S. Pat. No. 5,304,691, assigned to Shell, discloses a method of hydroformylating ethylene oxide to 3-hydroxypropanal and 1,3-propanediol in a single step using an improved catalyst system comprising a cobalt-tertiary phosphine ligand in combination with a ruthenium catalyst. In ""691 1,3-PDO and 3-HPA are produced by intimately contacting an oxirane, particularly ethylene oxide (hereafter EO), a ditertiary phosphine-modified cobalt carbonyl catalyst, a ruthenium catalyst promoter, and syngas (carbon monoxide and hydrogen) in an inert reaction solvent at hydroformylation reaction conditions. A PDO yield of up to 86-87 mole % is reported, using a catalyst comprising cobalt ligated with 1,2-bis (9-phosphabicyclononyl) ethane as bidentate ligand, and either triruthenium(0) dodecacarbonyl or bis[ruthenium tricarbonyl dichloride] as cocatalyst.
The production of 1,3-PDO in one step with minimal impurities and byproducts involves recycle and requires a catalyst system with good stability both during 1,3-PDO synthesis and during product recovery and recycle. It would be very desirable if a catalyst system were available that produced 1,3-PDO in one step, in good yields, and was characterized by greater oxidative stability during 1,3-PDO synthesis and recycle. In addition, phosphine ligands are relatively expensive and it would be desirable to have the option of a ligand system that provided the aforementioned advantages, but was less expensive.
In accordance with the foregoing, the present invention provides an alternative to the use of phosphine ligands in a hydroformylation catalyst composition. The ligands of the present invention provide a less expensive alternative, have the ability to form stable complexes with Group VIII transition metals, and provide good oxidative stability. The invention is a catalyst composition comprising:
a) A cobalt component comprising of one or more non-ligated cobalt carbonyl compounds; and
b) A ruthenium component comprising a ligated ruthenium carbonyl compound wherein said ligand is selected from a N-heterocyclic or multidentate N-heterocyclic moiety.
Bidentate and multidentate N-heterocyclics offer the potential advantages of greater oxidative stability, commercial availability (at least in certain cases), potentially lower cost, and the ability to form stable complexes with Group VIII transition metals. For example, 2,2xe2x80x2-dipyridyl-ruthenium complexes, among others, have been demonstrated to exhibit long-term stability under hydroformylation (synthesis gas pressure conditions).
The novel oxirane hydroformylation catalyst of the present invention involves a complex which is postulated to be a ruthenium-N-heterocylic ligand: cobalt complex. The characterizing feature of the new catalyst is the use of a bidentate or multidentate N-heterocyclic ligand ligated to ruthenium rather than cobalt, as is the case in U.S. Pat. No. 5,304,691.
The invention also provides a one step process for preparing a 1,3-diol, comprising the reaction of an oxirane with syngas at hydroformylation conditions in an inert solvent in the presence of the catalyst complex of this invention.